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Content for  TS 23.503  Word version:  17.5.0

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6.2  Network functions and entitiesWord‑p. 82

6.2.1  Policy Control Function (PCF)Word‑p. 82

6.2.1.1  GeneralWord‑p. 82

6.2.1.1.1  Session management related functionality |R16|Word‑p. 82
The PCF provides the following session management related functionality:
  • Policy and charging control for a service data flows;
  • PDU Session related policy control;
  • PDU Session event reporting to the AF.
The PCF provides authorized QoS for a service data flow and other network control regarding service data flow detection, gating, QoS and charging (except credit management) towards the SMF.
The PCF uses the service information received from the AF (e.g. SDP information or other available application information) and/or the subscription information received from the UDR to calculate the proper QoS authorization (QoS class identifier, bitrates). The PCF may also take into account the requested QoS received from the SMF and the analytics information (e.g. analytics related to "Service Experience") received from the NWDAF.
The PCF may check that the service information provided by the AF is consistent with both the operator defined policies and the related subscription information as received from the UDR during PDU Session establishment before storing the service information. The PCF may reject the request received from the AF when the service information is not consistent with either the related subscription information or the operator defined policies and may indicate, in the response to the AF, the service information that can be accepted by the PCF (e.g. the acceptable bandwidth). In the absence of other policy control mechanisms outside the scope of PCC, it is recommended that the PCF include this information in the response.
In this Release, the PCF supports only the interaction with a single AF for each AF session.
The Authorization of QoS shall be based on complete service information unless the PCF is required to perform the authorization of QoS based on preliminary service information. The PCF shall after receiving the complete service information, update the affected PCC rules accordingly.
At reception of the service information from the AF if configured through policy and taking into account information defined in TS 26.114, the PCF determines the Maximum Packet Loss Rate for UL and DL based on the service information and sends it to SMF along with the PCC rule.
The PCF supports usage monitoring control as described in clause 6.2.1.7.
The PCF supports sponsored data connectivity for a service as described in clause 6.2.1.8.
The PCF uses the information relating to subscriber spending available in the CHF as input for policy decisions related to e.g. QoS control, gating or charging conditions. Details for policy decisions based on spending limits are described in clause 6.1.3.17.
The PCF uses one or more pieces of information defined in the clause 6.2.1.2 as input for the selection of traffic steering policies used to control the steering of the subscriber's traffic as described in clause 6.1.3.14.
The PCF reports PDU Session events, e.g. Access Type, RAT Type (if applicable), Access Network Information, PLMN identifier where the UE is located, as described in clause 6.1.3.18.
The subscription and reporting of events when the target for reporting is an Internal Group Identifier or any UE accessing a combination of (DNN, S-NSSAI), is described in clause 5.2.5.7 of TS 23.502. The events that can be reported by the PCF are described in clause 6.1.3.18.
The subscription and reporting of events targeting an individual UE IP address (IPv4 address or IPv6 prefix) and optionally the DN information are described below. The events that can be reported by the PCF are described in clause 6.1.3.18.
The PCF shall ensure that the sum of the packet filters used by all PCC rules which trigger the generation of signalled QoS rules does not exceed the number of supported packet filters for signalled QoS rules indicated by the UE for the PDU Session, if this information is provided by the SMF (as defined in clause 6.2.1.2).
For EPC IWK, when PCF receives from the SMF of the report on UE resumed from suspend state, the PCF may provision PCC Rules to the SMF to trigger an IP-CAN Session modification procedure.
The PCF may provide the IP index as the PDU Session related policy to the SMF for IP address/Prefix allocation at SM Policy Association Establishment. If PCF receives from the SMF an allocated IP address/Prefix for the PDU Session, it shall not include IP Index into the PDU Session related policy.
On receiving the DN Authorization Profile Index provided by the SMF at the establishment or modification of the SM Policy Association for a PDU Session, the PCF takes the DN Authorization Profile Index as input for a policy decision and then obtains the list of PCC Rules (as defined in clause 6.3) and/or PDU Session related policy (as defined in clause 6.4) and provides them to the SMF as part of the Session Management Policy Control Data for enforcement.
On receiving the Session-AMBR provided by the SMF at the establishment or modification of the SM Policy Association for a PDU Session under the conditions defined in clause 5.6.6 of TS 23.501, the PCF provides the Authorized Session-AMBR as part of the PDU Session policy control information defined in clause 6.4.
The PCF provides DNAI(s) in the PCC rule(s) to the SMF, taking into account the AF request and the Local routing indication from the PDU Session policy control subscription information.
When the PCF detects that all PCC rules related to an AF session are removed, or the PCF detects that the SM Policy Association is terminated, the PCF shall request the AF to terminate the AF session. If the SMF indicated that the PCC rules were removed or that the SM Policy Association is terminated due to PS to CS handover, the PCF shall indicate PS to CS handover as cause within the request to terminate the AF session.
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6.2.1.1.2  Non-session management related functionality |R16|Word‑p. 83
The PCF provides the following non-session management related functionality:
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6.2.1.1.3  Network slice related functionality |R17|Word‑p. 83
The PCF provides the following network slice related functionality:
  • Limitation of the data rate per network slice (as described in clause 6.1.4).

6.2.1.2  Input for PCC decisionsWord‑p. 84

The PCF shall accept input for PCC decision-making from the SMF, the AMF, the CHF, the NWDAF if present, the UDR and if the AF is involved, from the AF, as well as the PCF may use its own predefined information. These different nodes should provide as much information as possible to the PCF. At the same time, the listed information below describes only examples of the information provided by the respective node and is not intended to be complete. Depending on the particular scenario all the information may not be available or is already provided to the PCF.
The AMF may provide information related to the UE as defined in clause 5.2.5.2 of TS 23.502, for example:
  • SUPI;
  • PEI of the UE;
  • Location of the subscriber;
  • Service Area Restrictions;
  • RFSP Index;
  • RAT Type;
  • GPSI;
  • Access Type;
  • Serving Network identifier (PLMN ID or PLMN ID and NID, see clause 5.34 of TS 23.501);
  • Allowed NSSAI;
  • UE time zone;
  • Subscribed UE-AMBR;
  • Mapping Of Allowed NSSAI;
  • S-NSSAI for the PDU Session;
  • Requested DNN.
The UE may provide information such as:
  • OSId;
  • List of PSIs;
  • Indication of UE support for ANDSP.
The SMF may provide information related to the PDU Session as defined in clause 5.2.5.4 of TS 23.502, for example:
  • SUPI;
  • PEI of the UE;
  • IPv4 address of the UE;
  • IPv6 network prefix assigned to the UE;
  • Default 5QI and default ARP;
  • Request type (initial, modification, etc.);
  • Type of PDU Session (IPv4, IPv6, IPv4v6, Ethernet, Unstructured);
  • Access Type;
  • RAT Type;
  • GPSI;
  • Internal-Group Identifier;
  • Location of the subscriber;
  • S-NSSAI;
  • DNN;
  • Serving Network identifier (PLMN ID or PLMN ID and NID, see clause 5.34 of TS 23.501);
  • Application Identifier;
  • Allocated application instance identifier;
  • Detected service data flow descriptions;
  • UE support of reflective QoS (as defined in clause 5.7.5.1 of TS 23.501);
  • Number of supported packet filters for signalled QoS rules for the PDU Session (indicated by the UE as defined in clause 5.7.1.4 of TS 23.501);
  • 3GPP PS Data Off status;
  • DN Authorization Profile Index (see clause 5.6.6 of TS 23.501);
  • DN authorized Session AMBR (see clause 5.6.6 of TS 23.501);
  • Satellite backhaul category information;
  • Provisioning Server address(es) (see clause 5.30 of TS 23.501).
The UDR may provide the information for a subscriber connecting to a specific DNN and S-NSSAI, as described in the clause 6.2.1.3.
The UDR may provide policy information related to an ASP as defined in clause 5.2.12.2 of TS 23.502, for example:
  • The ASP identifier;
  • A transfer policy together with a Background Data Transfer Reference ID, the volume of data to be transferred per UE, the expected amount of UEs.
The UDR may provide the service specific information as defined in clause 4.15.6.7 of TS 23.502.
The AF, if involved, may provide application session related information as defined in clause 5.2.5.3 of TS 23.502 directly or via NEF, e.g. based on SIP and SDP, for example:
  • Subscriber Identifier;
  • IP address of the UE;
  • Media Type;
  • Media Format, e.g. media format sub-field of the media announcement and all other parameter information (a= lines) associated with the media format;
  • Bandwidth;
  • Sponsored data connectivity information;
  • Flow description, e.g. source and destination IP address and port numbers and the protocol;
  • AF application identifier, i.e. an identifier that refers to the application the AF session belongs to;
  • DNN and possibly S-NSSAI;
  • AF Communication Service Identifier (e.g. IMS Communication Service Identifier), UE provided via AF;
  • AF Application Event Identifier;
  • AF Record Information;
  • Flow status (for gating decision);
  • Priority indicator, which may be used by the PCF to guarantee service for an application session of a higher relative priority;
  • Emergency indicator;
  • Application service provider;
  • DNAI;
  • Information about the N6 traffic routing requirements;
  • GPSI;
  • Internal-Group Identifier;
  • Temporal validity condition;
  • Spatial validity condition;
  • AF subscription for early and/or late notifications about UP management events;
  • AF transaction identifier;
  • TSC individual QoS information as described in clause 6.1.3.22;
  • QoS information to be monitored;
  • Service area coverage;
  • Indication that high throughput is desired;
  • Reporting frequency;
  • User Plane Latency Requirement.
The AF may provide BDT related information as defined in clause 5.2.5.5 of TS 23.502 via NEF, for example:
  • Background Data Transfer Reference ID;
  • BDT Policy;
  • Volume per UE;
  • Number of UEs;
  • Desired time window;
  • Network Area Information.
The CHF, if involved, may provide the following information for a subscriber as defined in clause 5.2.5.17 of TS 23.502, for example:
  • Policy counter status for each relevant policy counter.
The NWDAF, if involved, may provide analytics information as described in clause 6.1.1.3.
In addition, the predefined information in the PCF may contain additional rules based on charging policies in the network, whether the subscriber is in its home network or roaming, depending on the QoS Flow attributes.
The 5QIs (see clause 5.7.4 of TS 23.501) in the PCC rule is derived by the PCF from AF or UDR interaction if available. The input can be SDP information or other available application information, in line with operator policy.
The Allocation and Retention Priority in the PCC Rule is derived by the PCF from AF or UDR interaction if available, in line with operator policy.
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6.2.1.3  Policy control subscription information managementWord‑p. 87

The PCF may request subscription information at PDU Session establishment, PDU Session modification and during the UE Policy Association Establishment procedure.
The PCF may receive notifications on changes in the subscription information. Upon reception of a notification, the PCF shall make the policy control decisions necessary to accommodate the change in the subscription and shall update the SMF and/or the AMF if needed.
The policy control subscription profile information provided by the UDR during the UE Policy Association Establishment procedure using Nudr service for Data Set "Policy Data" and Data Subset "UE context policy control data" is described in Table 6.2-1:
Information name Description Category
Subscriber categoriesList of category identifiers associated with the subscriberOptional
Tracing RequirementsTracing requirements as defined in TS 32.421Optional
PEIThe Permanent Equipment Identifier of the UE.Optional
OSIdIdentifies the operating system supported by UE.Optional
Indication of UE support for ANDSPIndicates the UE support for ANDSP.Optional
S-NSSAI subscription informationContains the list of subscribed S-NSSAIs, its associated subscribed DNNs. For each DNN, it includes the Allowed PDU Session types, the Allowed SSC modes and the ATSSS information (NOTE).Optional
NOTE:
ATSSS information is defined in TS 23.502 Table 5.2.3.3.1-1 and indicates whether MA PDU Session establishment is allowed.
The policy control subscription profile information provided by the UDR at PDU Session establishment, using Nudr service for Data Set "Policy Data" and Data Subset "PDU Session policy control data" is described in Table 6.2-2.
Information name Description Category
Allowed servicesList of subscriber's allowed service identifiersOptional
Subscriber categories List of category identifiers associated with the subscriberOptional
Subscribed GBRMaximum aggregate bitrate that can be provided across all GBR QoS Flows for the DNN and S-NSSAI.Optional
ADC supportIndicates whether application detection and control can be enabled for a subscriberOptional
Subscriber spending limits controlIndicates whether the PCF must enforce policies based on subscriber spending limitsOptional
IP index informationInformation that identifies the IP Address allocation method during PDU Session establishmentOptional
Background Data Transfer Reference ID(s)Reference ID(s) for Background Data Transfer Policies that apply to the UE.Optional
Local routing indicationIndication on whether AF influence on traffic routing is allowed or not allowedOptional
Subscribed UE-Slice-MBRSubscribed UE-Slice-MBR value per S-NSSAIConditional (NOTE 2)
Charging related informationThis part defines the charging related information in the policy control subscription profile
Default charging methodDefault charging method for the PDU Session (online / offline)Optional
CHF addressThe address of the Charging Function and optionally the associated CHF instance ID and CHF set ID (see clause 6.3.1.0 of TS 23.501)Optional
Usage monitoring related informationThis part includes a list of usage monitoring profiles associated with the subscriber. Each usage monitoring profile is logically associated with a particular operator offer, and includes the following elements
Monitoring keyAn identifier to a usage monitoring control instance that includes one or more PCC rulesConditional (NOTE 1)
Usage monitoring levelIndicates the scope of the usage monitoring instance (PDU Session level or per Service)Optional
Start dateStart date and time when the usage monitoring profile appliesOptional
End dateEnd date and time when the usage monitoring profile appliesOptional
Volume limitMaximum allowed traffic volumeOptional
Time limitMaximum allowed resource time usageOptional
Reset periodTime period to reset the remaining allowed consumed usage for periodic usage monitoring control (postpaid subscriptions)Optional
MPS subscription dataThis part defines the MPS subscription information in the policy control subscription profile
MPS priorityIndicates subscription to MPS priority service; priority applies to all traffic on the PDU SessionConditional (NOTE 1)
IMS signalling priorityIndicates subscription to IMS signalling priority service; priority only applies to IMS signalling trafficConditional (NOTE 1)
MPS priority levelRelative priority level for multimedia priority servicesConditional (NOTE 1)
MCS priorityIndicates subscription to MCS priority service; priority applies to all traffic on the PDU SessionConditional (NOTE 1)
MCS priority levelRelative priority level for MCS servicesConditional (NOTE 1)
NOTE 1:
The information is mandatory if the specific part is included in the subscription information (e.g. the monitoring key is mandatory if the usage monitoring information part is included).
NOTE 2:
The information is used in PCF as described in clause 6.2.1.9 when the monitoring of the UE-Slice-MBR for an S-NSSAI is performed at the PCF. There may be a UE-Slice-MBR value for each S-NSSAI, if applicable.
Information name Description Category
Remaining allowed usage related informationThis part includes a list of Remaining allowed usage associated with the subscriber.
Monitoring keyAn identifier to a usage monitoring control included one or more PCC rulesConditional (NOTE 1)
Usage monitoring levelIndicates the scope of the usage monitoring (PDU Session level or service level)Optional
Volume usageRemaining allowed traffic volumeOptional
Time usageRemaining allowed resource time usageOptional
NOTE 1:
The information is mandatory if the specific part is included in the subscription information (e.g. the monitoring key is mandatory if the usage monitoring information part is included).
The Allowed services may comprise any number of service identifiers allowed for the subscriber in the PDU Session. The PCF maps those service identifiers into PCC rules according to local configuration and operator policies.
The Subscriber category may comprise any number of identifiers associated with the subscriber (e.g. gold, silver, etc.). Each identifier associates operator defined policies to the subscriber that belong to that category.
The Usage monitoring related information may comprise any number of usage monitoring control instances associated with the subscriber. In each usage monitoring control instance is mandatory to include the Monitoring key. The Reset period only applies to usage monitoring control instances that periodically reset the allowed usage (e.g. daily, monthly, etc.). If the Reset period is not specified, the usage monitoring control instance ends when the allowed data is consumed or when the End date is reached. The usage monitoring related information is used by the PCF instead of the respective information for the subscriber category.
The policy subscription profile may be extended with operator-specific information. Operator-specific extensions may be added both to any specific part of the policy control subscription information (e.g. to the subscriber category part), or as a new optional information block.
Handling of operator specific policy data by the PCF is out of scope of this specification in this release.
The policy control subscription profile information provided by the UDR during the UE Policy Association Establishment procedure using Nudr service for Data Set "Policy Data" and Data Subset "Policy Set Entry" is described in Table 6.2-4.
Information name Description Category
Policy Set EntryList of PSIs and content for each PSI. Content may be Access Network Discovery & Selection Policy Information or UE Route Selection Policy information or both.Optional
The network slice specific policy control information is per S-NSSAI information stored by the UDR and updated by the PCF during PDU Session Establishment or Modification procedure using Nudr service for Data Set "Policy Data" and Data Subset "Network Slice Specific Control Data" is described in Table 6.2-5:
Information name Description Category
Maximum Slice Data Rate for UL (per S-NSSAI)The maximum uplink data rate for the specific network sliceOptional (NOTE 2)
Maximum Slice Data Rate for DL (per S-NSSAI)The maximum downlink data rate for the specific network sliceOptional (NOTE 2)
Remaining Maximum Slice Data Rate for UL (per S-NSSAI)The remaining maximum uplink data rate for the specific network slice (NOTE 1).Optional (NOTE 3)
Remaining Maximum Slice Data Rate for DL (per S-NSSAI)The remaining maximum downlink data rate limited for a specific network slice (NOTE 1).Optional (NOTE 3)
NOTE 1:
The initial value is set to the Maximum Slice Data Rate for UL/DL value.
NOTE 2:
The information is only used for limitation of data rate per network slice with assistance of the NWDAF.
NOTE 3:
The information is only used for limitation of data rate per network slice with PCF based monitoring.
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6.2.1.4  V-PCFWord‑p. 90

The V-PCF is a functional element that encompasses policy control decision functionalities in the VPLMN.
For session management related policy control, the V-PCF only includes functionality for local breakout roaming scenario based on roaming agreements.
For UE policy control, the V-PCF receives the UE policy from the H-PCF and forwards it to the UE via the AMF. The V-PCF can send additional UE policy information (i.e. ANDSP policies) to the UE which is different from the one from H-PCF.
For Access and mobility related policy control, the V-PCF generates the values for RFSP Index, UE-AMBR, UE-Slice-MBR, Service Area Restriction and SMF selection management.
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6.2.1.5  H-PCFWord‑p. 90

The H-PCF is a functional element that encompasses policy control decision functionalities in the HPLMN.
For session management related policy control, the H-PCF only includes functionality for home routed roaming scenario and provides the same functionality as the PCF in the non-roaming case.
For UE policy control, H-PCF generates the UE policy based on subscription data and transfers the UE policy to the UE via the AMF, or via the V-PCF in the roaming case.

6.2.1.6  Application specific policy information managementWord‑p. 90

The application specific information used for policy control includes:
  • Negotiation of BDT information stored in the UDR as Data Set "Policy Data" and Data Subset "Background Data Transfer data": It contains an ASP identifier, Non-IP information or IP 3-tuple to identify the Application server, a transfer policy together with the Background Data Transfer Reference ID, the volume of data to be transferred per UE, the expected amount of UEs and optionally, the subscription to notifications when the BDT policy needs to renegotiated;
  • Sponsored data connectivity profile information stored in the UDR as Data Set "Policy Data" and Data Subset "Sponsored data connectivity profile data": It contains a list of ASP identifiers and their applications per sponsor identity;
  • Application Function request information for multiple UEs (per group of UEs or all UEs) stored in the UDR as Data Set "Application Data" and Data Subset "AF request information for multiple UEs".
The application specific policy information may be requested/updated by the PCF per AF request.
The management of Application Function request information for multiple UEs is defined in clause 6.3.7.2 of TS 23.501, the management of policies for the negotiation of BDT is defined in clause 6.1.2.4 of this specification and the provision and usage of sponsored data connectivity profile is defined in clause 6.2.1.1 of this specification.
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6.2.1.7  Usage monitoring |R16|Word‑p. 91

The PCF supports usage monitoring control for a PDU Session or per Monitoring Key. Usage is defined as either volume or time of user plane traffic.
The PCF may receive usage monitoring related information per DNN and S-NSSAI combination and UE from the UDR, i.e. the overall amount of allowed resources (based either on traffic volume and/or traffic time) that are to be monitored for the PDU Sessions of a user, together with the corresponding remaining allowed usage related information. In addition, usage monitoring related information for Monitoring key(s) per DNN and S-NSSAI combination and UE may also be received from the UDR, together with the corresponding remaining allowed usage related information. For the purpose of usage monitoring per access type, the PCF receives an individual Monitoring key per access type from UDR. Details about the usage monitoring related information and the remaining allowed usage related information provided by the UDR are described in clause 6.2.1.3.
For the purpose of usage monitoring control the PCF shall request the Usage report trigger and provide the necessary usage threshold(s), either volume threshold, time threshold, or both volume threshold and time threshold, upon which the SMF shall report to the PCF. The PCF shall decide if and when to activate usage monitoring to the SMF.
The PCF may provide a Monitoring time to the SMF for the Monitoring keys(s) and optionally specify a subsequent threshold value for the usage after the Monitoring time.
If the SMF reports usage before the Monitoring time is reached, the Monitoring time is not retained by the SMF. Therefore, the PCF may again provide a Monitoring time and optionally the subsequent threshold value for the usage after the Monitoring time in the response.
It shall be possible for the PCF to request a usage report from the SMF.
Once the PCF receives a usage report from the SMF the PCF shall deduct the value of the usage report from the remaining allowed usage for that DNN and S-NSSAI combination and UE (if usage per PDU Session is reported). If usage is reported from the SMF, the PCF shall deduct the value of the usage report from the remaining allowed usage for individual Monitoring key(s) for that DNN and S-NSSAI combination and UE (if usage for one or several Monitoring keys is reported).
If the remaining allowed usage reaches a value of zero (or below zero), the PCF may apply other policy decisions and interact with the SMF accordingly.
If the SMF reports usage for a certain Monitoring key and if monitoring shall continue for that Monitoring key then the PCF shall provide new threshold value(s) in the response to the SMF respectively. If Monitoring time and subsequent threshold value are used then the PCF provides them to the SMF as well.
The PCF may provide a new volume threshold and/or a new time threshold to the SMF, the new threshold values overrides the existing threshold values in the SMF.
If monitoring shall no longer continue for that Monitoring key, then the PCF shall not provide a new threshold in the response to the SMF.
If the last PDU Session of a user for a DNN and S-NSSAI combination is terminated, the PCF shall store the remaining allowed usage, i.e. the information about the remaining overall amount of resources, in the UDR.
If the End date of the usage monitoring related information (see clause 6.2.1.3 for details) is reached, the PCF shall reset the remaining allowed usage to the value(s) indicated in the usage monitoring related information and shall then interact with the SMF to undo any previously applied policy decisions related to remaining allowed usage of zero (or below zero).
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6.2.1.8  Sponsored data connectivity |R16|Word‑p. 92

The PCF may authorise an application service provider to request specific PCC decisions (e.g. authorisation to request sponsored IP flows, authorisation to request QoS resources) based on sponsored data connectivity profile from the UDR. For sponsored data connectivity, the PCF may receive a usage threshold from the AF. If the AF specifies a usage threshold, the PCF shall use the Sponsor Identity to construct a Monitoring key for monitoring the volume, time, or both volume and time of user plane traffic, and invoke usage monitoring on the SMF. The PCF shall notify the AF when the SMF reports that a usage threshold for the Monitoring key is reached provided that the AF requests to be notified for this event, as described in clause 6.1.3.18. If the usage threshold is reached, the AF may terminate the AF session or provide a new usage threshold to the PCF. Alternatively, the AF may allow the session to continue without specifying a usage threshold. If the AF decides to allow the session to continue without specifying a usage threshold, then monitoring in the SMF shall be discontinued for that monitoring key by the PCF, unless there are other reasons for continuing the monitoring.
If the H-PCF detects that the UE is in a home-routed roaming scenario when sponsored data connectivity is requested by an AF, it may allow the sponsored data connectivity in the service authorization request, reject the service authorization request, or initiate the AF session termination based on home operator policy.
If the AF revokes the service information and the AF has notified previously a usage threshold to the PCF, the PCF shall report the usage up to the time of the revocation of service authorization.
If the PDU Session terminates and the AF has specified a usage threshold then the PCF shall notify the AF of the accumulated usage (i.e. either volume, or time, or both volume and time) of user plane traffic since the last usage report.
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6.2.1.9  Monitoring the data rate per Network Slice for a UE |R17|Word‑p. 92

A PCF may support monitoring of data rate per S-NSSAI for a UE. The monitoring is performed by aggregating the Session-AMBR values and the MBR values allocated to each PCC Rule (belonging to a GBR service data flow) in all PDU Sessions established for a UE in that S-NSSAI. To enable this monitoring, the SMF selects the same PCF instance for all PDU Sessions of the UE to the S-NSSAI that is subject to this monitoring, this is achieved as described in clause 6.3.7.1 of TS 23.501, for example by using local operator policies in the SMF, SUPI ranges or explicit indication from the AMF to select the PCF selected for the UE.
If the monitored data rate per S-NSSAI for a UE reaches a certain percentage of the UE-Slice-MBR value for that S-NSSAI (detected via operator defined thresholds), the PCF may apply a policy decision to strengthen the traffic restrictions for individual PDU Sessions or PCC rules (e.g. to change Session-AMBR value (if allowed by the HPLMN) or update PCC Rule(s) to change QoS or charging keys(s)) and interact with the SMF accordingly. When the data rate per S-NSSAI for a UE falls below that percentage of the UE-Slice-MBR value, the PCF may relax the traffic restrictions for individual PDU Sessions or PCC rules.
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6.2.1.10  Monitoring the data rate per Network Slice |R17|Word‑p. 92

6.2.1.10.1  GeneralWord‑p. 92
The PCF supports monitoring and limitation of the data rate per S-NSSAI.
If the S-NSSAI is subject to network slice data rate limitation the Remaining Maximum Slice Data rate per S-NSSAI is stored in the UDR as Data Set "Policy Data" and Data Subset "Network Slice Specific Policy Control Data" as defined in clause 6.2.1.3.
The PCF interacts with the UDR to update the network slice specific policy control information per S-NSSAI in the UDR, i.e. the Remaining Maximum Slice Data Rate per S-NSSAI, so that the usage of multiple PCFs for the same S-NSSAI is enabled.
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6.2.1.10.2  Monitoring the data rate per Network Slice by using QoS parametersWord‑p. 93
For the purpose of monitoring the data rate per S-NSSAI, the PCF shall perform the following for an SM Policy Association with an S-NSSAI subject to data rate limitation:
  • At the establishment of a SM Policy Association, the PCF shall check whether the Remaining Maximum Slice Data Rate is higher than the Authorized Session-AMBR. If so, the PCF shall deduct the value of the Authorized Session-AMBR allocated to the PDU Session from the Remaining Maximum Slice Data Rate for that S-NSSAI in the UDR. If the Remaining Maximum Slice Data Rate is not sufficient, the PCF shall reject the establishment of the SM Policy Association.
  • At the time a PCC Rule of a GBR service data flow is installed, modified or activated in the SMF, the PCF requests reporting "Successful resource allocation" with the corresponding Policy Control Request Trigger. When the SMF reports that the resources are successfully allocated, the PCF shall deduct the value of the MBR authorized for the GBR service data flow from the Remaining Maximum Slice Data Rate for that S-NSSAI in the UDR.
  • At the time a change of Authorized Session-AMBR occurs or a PCC Rule containing a GBR value is removed or modified, the PCF shall update the Remaining Maximum Slice Data Rate for that S-NSSAI in the UDR accordingly.
  • If the Remaining Maximum Slice Data Rate for that S-NSSAI reaches a (operator defined) threshold that indicates that it is closer to zero, the PCF may apply a policy decision to strengthen the traffic restrictions for individual PDU Sessions or PCC rules (see clause 6.1.4.1) and interact with the SMF accordingly. When the Remaining Maximum Slice Data Rate for that S-NSSAI increases again, the PCF may relax the traffic restrictions for individual PDU Sessions or PCC rules.
  • At the time the SM Policy Association for an S-NSSAI subject to data rate limitation is terminated, the PCF shall add the value of the Authorized Session-AMBR allocated to the PDU Session to the Remaining Maximum Slice Data Rate for that S-NSSAI in the UDR.
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